Multi-layer film structure for use with a high-speed pouch forming, filling and sealing machine

ABSTRACT

The multi-layer film structure having an inner sealing layer which comprises metallocene resin, a core which includes polypropylene copolymer and an outer layer and wherein the multi-layer film structure has a thickness within a range between about 50 and 70 microns (2.0-2.75 mil). By utilizing this thin film with specific properties the sealers may be operated at lower temperatures thereby resulting in an energy saving and they produce seals having improved seal strength of 30% to 50% as compared with known prior mono-layer polyethylene film. The seal initiation temperature is reduced by 10° C. to 15° C. and the film exhibits an improved machine direction tensile strength of 25% to 40% and an improvement of 30% to 50% in puncture resistance as compared with a 76 microns (3 mil) mono-layer polyethylene film. This results in a reduction in the sealing cycle time and an increase in the throughput of the machine. This results in a liquid pouch having a substantial improvement in drop test performance, puncture resistance and seal strength. The machine accomplishes better seals with less energy, requires less downtime for roll changes and maintenance and increase throughput.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of Application Ser. No.09/313,112, filed May 27, 1999.

TECHNICAL FIELD

[0002] The present invention relates to a multi-layer film structurecomprised of an inner sealing layer, an outer layer and a coresandwiched between the sealing layer and the outer layer, and whereinthe film structure is particularly for use in a high-speed pouchforming, filling and sealing machine.

BACKGROUND ART

[0003] Traditionally, in North America, the film used for packagingfluid milk or the like in flexible plastic pouches consists of a 76microns (3 mil) mono-layer polyethylene film.

[0004] However, this standard film has some disadvantages which shouldbe overcome. For example, the packaging operation requires a certainamount of electrical energy for the heat sealing operation due to thethickness of the film. To generate this heat electrical energy isdispensed. It is desirable to develop a process which could decrease theenergy consumption in order to make the operation more economicallyfeasible. Another problem involved with the sealing operation is thatsome of the hardware, such as the sealing element per se and the rubberand Teflon™ parts associated with the sealing jaws have a relativelyshort useful life, requiring frequent changes and again increasing thecost of producing milk pouches.

[0005] Yet another problem resulting from the packaging of liquids witha mono-layer polyethylene film is the amount of waste and machinedowntime due to film roll changes and seal breaks. Packaging milk orother liquids with mono-layer polyethylene also involves the use of anarrow sealing window which renders the operation somewhat difficult.Finally, the seals obtained with this type of film pouches, oftenexhibits weakness which can cause fluid leakage.

[0006] Polymer film pouches made from a polyethylene film structure andused for packaging flowable materials such as milk, are known andexamples of such are described in U.S. Pat. Nos. 5,288,531; 5,360,648;5,364,486 and 5,508,051, all of which have issued to the Down ChemicalCompany.

SUMMARY OF INVENTION

[0007] It is a feature of the present invention to provide a thinnermulti-layer coextruded film structure, which overcomes some or all ofthe disadvantages of the prior art and incorporated in a bag forming,sealing and filling machine to improve on its method of operation andthroughput.

[0008] It is another feature of the present invention to provide fluidcontaining pouches that exhibit desirable properties as compared to thepouches of the prior art.

[0009] It is another feature of the invention to provide a multi-layerfilm structure which makes it possible to reduce the material used ascompared to the film of the prior art.

[0010] It is another feature of the present invention to provide amulti-layer film structure for packaging liquid that can be sealed atmuch lower seal initiation temperature.

[0011] It is another feature of the present invention to provide amulti-layer film structure for packaging liquid that has a greatermachine direction tensile strength.

[0012] It is another feature of the present invention to provide a pouchmade with the multi-layer film structure according to the invention thatis improved in horizontal seal strength, exhibits lower horizontal sealthinning, and minimizes post consumer waste.

[0013] It is yet another feature of the present invention to provide alower gauge pouch having a higher stiffness enabling pouring of liquid,and which exhibits a substantial improvement in drop test performanceand puncture resistance.

[0014] It is another feature of the present invention to provide amulti-layer film structure for packaging liquid into pouches, whichensures a reduction of the electrical energy required for sealing due tolower heat initiation temperature and lower mass to be sealed.

[0015] It is another feature of the present invention to provide amulti-layer film structure for packaging consumable liquid products intopouches which uses lower sealing temperature and thereby improves theuseful life of the jaw sealers, such as the rubber, and electricalsealing heads, and resulting in overall energy reduction.

[0016] It is another feature of the present invention to provide amulti-layer film structure for packaging dairy products into pouchesthat permits a substantial reduction of wastes and downtime caused byfilm roll changes.

[0017] It is another feature of the present invention to provide amulti-layer film structure for packaging liquid wherein sealing iseasier to operate due to a wider sealing window, and speed increase ismade possible as a result of a faster sealing cycle.

[0018] According to another feature of the present invention there isprovided a high-speed pouch forming, sealing and filling machine and itsmethod of operation and utilizing sealing heads which operate at lowertemperatures due to a decrease in the film thickness as compared with 76microns (3 mil) mono-layer polyethylene film and thereby resulting in anelectrical energy saving and wherein the thin film permits the machineto obtain a substantially higher yield with a film roll substantiallythe same size as with the 76 microns (3 mil) film.

[0019] According to the above features, from a broad aspect, the presentinvention provides a multi-layer structure for use in packagingconsumable liquid into flexible pouches comprising an inner sealinglayer, an outer layer, and a core sandwiched between said sealing layerand said outer layer, wherein the sealing layer comprises about 40% to100% weight percent of a metallocene resin having a density of betweenabout 0.902 and 0.912, and about 0 to 60 weight percent of a low densitypolyethylene or a mixture of low density polyethylene and linear lowdensity polyethylene, the outer layer comprises a low densitypolyethylene or a mixture of low density polyethylene and linear lowdensity polyethylene, the core comprising a mixture of about 20 to 90weight percent of a polypropylene copolymer and about 10 to 80 weightpercent of a low density polyethylene or a mixture of low densitypolyethylene and linear low density polyethylene, said multi-layerstructure having a thickness within a range between about 50 and 70microns (2.0-2.75 mil).

[0020] According to a still further broad aspect of the presentinvention there is provided a high-speed pouch forming, sealing andfilling machine which comprises means to draw a multi-layer film from afilm roll over a pouch-former to form a plastic film tube having anoverlap vertical film edge. A vertical sealer is provided and has asealing head for heat fusing the overlap vertical film edge to form avertical seal. A filler tube extends into the plastic film tube forinjecting a consumable liquid product at a filling location of theplastic film tube. A horizontal sealing jaw, having an electricalthermal sealing element, is provided for effecting a horizontal sealacross the plastic film tube and spaced below the filling location andfor simultaneously severing the tube to form a top transverse seal for afilled pouch and a bottom transverse seal for a pouch being filled. Themulti-layer film has an inner sealing layer, an outer layer and a coresandwiched therebetween. The characteristics of this film are describedabove. The horizontal and vertical seals have an improved seal strengthof 30% to 50% as compared with the 76 microns (3 mil) mono-layerpolyethylene film and a 10° C. to 15° C. reduction in seal initiationtemperature, an improved machine direction tensile strength of 25% to40% and an improvement of 30% to 50% in puncture resistance, whilereducing the sealing cycle time and increasing the throughput of themachine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The preferred embodiments of the present invention will now bedescribed with reference to the accompanying drawings in which:

[0022]FIG. 1 is a schematic diagram illustrating basic component partsof the improved high-speed pouch forming, sealing and filling machine ofthe present invention;

[0023]FIG. 2a is an enlarged fragmented and partly sectioned viewshowing the horizontal sealing jaws of a prior art machine and thedefect of seal thinning that occurs when using conventional 76 microns(3 mil) mono-layer polyethylene film;

[0024]FIG. 2b is an enlarged sectional view of the horizontal seal ofthe pouch illustrated in FIG. 2a which better illustrates seal thinning;

[0025]FIG. 3 is a sectional view illustrating the three-layer film ofthe present invention; and

[0026]FIG. 4 is an enlarged fragmented sectional view showing a tophorizontal seal formed on a pouch and using the three-layer film of thepresent invention and wherein film thinning is eliminated.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0027] Referring now to the drawings and more particularly to FIG. 1there is shown generally at 10 basic component parts of a high-speed bagforming, sealing and filling machine constructed in accordance with thepresent invention. These basic component parts are only schematicallyillustrated and are well known in the art. The improvement in themachine resides primarily in the vertical sealer operatingcharacteristics and the horizontal sealing jaws characteristics, as willbe described later. The sealers are controlled to operate with a newmulti-layer film whereby to increase the throughput of the machine andprovide filled pouches having improved strength and wherein the sealsare greatly improved over those of the prior art thereby resulting in amachine which can output more filled pouches, achieve a significantwaste reduction and less downtime as compared with prior art machinesusing a 76 microns (3 mil) mono-layer polyethylene film. As hereinshownthe high-speed pouch forming, sealing and filling machine comprises afilm roll 11 provided with a multi-layer film 12 which is guided throughguide rolls and tensor rolls 13 to a top end of a pouch former 14 wherethe plastic film is guided and folded to form a plastic film tube 15having an overlap vertical film edge 16. A filler tube 17 extends withinthe pouch former 14 and the tube 15 and has a liquid discharge end 17′positioned at a filling location 18.

[0028] A vertical sealer 19 has a sealing head 20 provided with aheating element 21 and a backing member 22 is disposed verticallyaligned behind the overlap vertical film edge 16. A vertical seal isformed by fusing the overlapped edge 16 along the plastic tube 15 abovethe filling location 18. A horizontal sealing jaw assembly 23 isprovided spaced at a predetermined distance below the filling location18 whereby to form a horizontal seal across the film tube 18 and at thesame time sever the tube to form a sealed pouch 24 filled with aconsumable liquid 25 therein. The pouch is then released on a dischargeconveyor means 26.

[0029] The horizontal sealing jaw assembly 23 is comprised of a sealinghead 27 provided with an electrical impulse sealing wire element 28 tosever the film tube as well as to form a top horizontal seal 29 for thepouch 24 and a bottom horizontal seal 30 for the next pouch being formedherein illustrated by reference numeral 24′. The horizontal sealing jawassembly 23 also has a backing member 31 which is provided as a rubberor Teflon™ pad 32 to serve as a backing for the electrical impulsesealing wire element 27. From time-to-time it is necessary to change thepad and the wire element as they wear down. By operating at lowertemperature, 10° C.-15° C. lower than the prior art discussed above,these elements have a longer life cycle and there is less machinestoppages. The jaw assembly 23 may move in and out in unison to form theseal or the backing member 31 may be stationary and positioned close tothe film with only the sealing head 26 moving in and out. Other suitablesealing assemblies are conceivable provided they can achieve the sameresults. The film sheet 12 is drawn in continuous motion by a pair ofdraw rolls 33 in a manner well known in the art. So far we havedescribed the basic component parts of a well known pouch forming,sealing and filling machine such as the Thimonnier M3200™ or a PrepakIS-7™.

[0030] The present invention resides in the provision of a novelmulti-layer film structure in combination with the machine to enhancethe performance of the machine. This enhancement is achieved bycontrolling the temperature of the sealing assemblies 19 and 23 whereinthey operate at temperatures which are lower than prior art machines.The draw rolls 33 are also operated at higher speeds whereby to increasethe throughput of the machine while producing horizontal seals which aremuch superior than the above-mentioned prior art machines and resultingin a production having less post consumer waste and permitting themachine to operate with less downtime previously caused by malfunctionor plastic film roll change.

[0031] In particular the high-speed bag forming, sealing and fillingmachine as above described is utilized for the production of milkpouches and such machines conventionally use a 76 microns (3 mil)mono-layer polyethylene film which heretofore was the best film productavailable for this use. FIGS. 2a and 2 b illustrate one of the moreserious problems that these machines have been plagued with in theproduction of such pouches and namely the formation of seal thinning. Asshown in FIG. 2a the pouch 24 has just been formed with the horizontalseal 29 severed and the filled pouch 24 is being discharged under theinfluence of its own weight. As the seal is formed the weight of theliquid 25 within the pouch 24 exerts a load on the horizontal seal andthis causes seal thinning in the region 35. Seal thinning is caused bythe stretching of the polyethylene in the area of the seal which causesthe film to thin out in this region. FIG. 2b better illustrates the sealthinning area 35 and as hereinshown this produces a weakness in thepouch 24 in this thinner stretched area of the seal. As the pouch isdropped on the discharge conveyor 26 it is subject to impact which couldburst the film in the seal thin region 35. Furthermore, as these pouchesare handled by consumers or during packaging pressures applied againstthe liquid 25 within the pouch exerts a force on the thin film region 35which again could cause leakage. Weak seals caused by seal thinning haslong existed and no adequate solution has been found to date to improvethese machines and the film in order to substantially overcome theabove-mentioned problems. We have now discovered that by producing afilm which can substantially eliminate seal thinning and improve onmachine performance that a superior pouch can be produced at a highermachine throughput and at a lower cost by substantially eliminating theabove production problems.

[0032] In a preferred embodiment the multi-layer film of the presentinvention is a three-layer film as schematically illustrated in FIG. 3.The three-layer film has an inner sealing layer 36, an outer layer 37and a core layer 38 sandwiched therebetween. The core may be of one ofseveral layers of polymers.

[0033] Seal thinning is substantially eliminated by the combination ofthe m-polyethylene sealing layer and a core incorporating a highermelting point polypropylene.

[0034] According to preferred embodiments, the sealing layer 36represents about 10 to 30 weight percent of the structure, the core 38represents about 30 to 70 weight percent of the structure, and the outerlayer 37 represents about 10 to 30 weight percent of the structure.

[0035] Preferably, the sealing layer 36 is a metallocene resin having adensity within a range between about 0.902 and 0.905, and the thickness“x” of the multi-layer structure is preferably about 65 microns.

[0036] In accordance with another embodiment, the multi-layer structurehas an inner layer 36 having a seal initiation temperature between about80° and 90° C.

[0037] The metallocene resin preferably consists of m-polyethylene. Forexample, the sealing layer may comprise between about 70 and 95 weightpercent metallocene polyethylene, more specifically between about 75 and85 weight percent metallocene polyethylene.

[0038] The preferred copolymer to be used in the core 38 consists ofhigh impact polypropylene copolymer having a melting point differentialwith the m-polyethylene of at least 40° C.

[0039] The invention also relates to a process for preparing themulti-layer structure by providing a sealing composition comprisingabout 40 to 100 weight percent of a metallocene resin having a densitybetween about 0.902 and 0.912, and about 0 to 60 weight percent of a lowdensity polyethylene or a mixture of low density polyethylene and linearlow density polyethylene, an outer layer composition comprising a lowdensity polyethylene or a mixture of low density polyethylene and linearlow density polyethylene, and a core composition comprising a mixture ofabout 20 to 90 weight percent of a polypropylene copolymer and about 10to 80 weight percent of a low density polyethylene or a mixture of lowdensity polyethylene and linear low density polyethylene, simultaneouslyco-extruding in a blown or cast coextrusion line, the sealingcomposition, the outer layer composition and the core composition, andfeeding the co-extruded compositions to a die under conditions toprovide a thickness between about 50 and 70 microns.

[0040] When compared to the traditional 76 microns (3 mil) mono-layerfilm, the advantages of the film according to the invention when used invertical form, fill & seal machine, such as shown in FIG. 1, for aliquid pouch application are as follows:

[0041] Film:

[0042] a minimum of 25% improvement in yield (sq.inch per lbs)

[0043] a 10° C. to 15° C. lower seal initiation temperature

[0044] 25% to 40% greater machine direction tensile strength (Psi)

[0045] 30% to 50% improvement in puncture resistance (lbs/mil)

[0046] Pouch:

[0047] a 30% to 50% improvement in horizontal seal strength (lb/inch)

[0048] a reduction of horizontal seal thinning from more than 20% toless than 3% (typical seal thinning is greater than 20% for mono-layerfilms in this application)

[0049] a minimum of 25% post consumer waste reduction

[0050] an improvement of 30% to 50% in stiffness, (% modulus in Psi)which enables pouring of liquid at a lower gauge

[0051] a two to threefold improvement in drop test performance

[0052] Pouch filling and sealing application

[0053] a 20% to 40% reduction of energy required for sealing due to thelower heat initiation temperature and the lower mass (33% less) to sealthrough

[0054] an improvement in the useful life of consumable itemsproportional to the energy reduction (rubber, Teflon™, sealing element)

[0055] a minimum of 20% reduction of wastes and downtime caused by filmroll changes

[0056] easier operation due to a wider sealing window

[0057] increased speed made possible by a faster sealing cycle

[0058]FIG. 4 illustrates the improvement in the seal of the pouch 24″achieved with the multi-layer film of the present invention. As can beseen seal thinning below the top horizontal seal 29′ is eliminated andresults in a pouch which is free of seal defects and which exhibits allof the above listed advantages of the pouch as well as the machine.Although the three-layer film of the present invention has beendescribed with particular reference to a pouch forming sealing andthinning machine such as a VFFS machine like a Thimonnier M3200™ orPrepak IS-7™, it is conceivable that this film may have other uses andthe present invention is not intended to limit the scope of its use insuch machines.

[0059] The invention will now be illustrated by means of the followingtable which is not intended to limit the scope of the invention asdefined in the appended claims. DG 2 DG 10 Comp 1 Comp 2 Thickness (mil)2.5 2.5 3.0 3.0 Film Yield 13,400    13,400    10,200    10,200    SealInitiation Temperature (≡C) 80 80 95 95 Puncture (peak load in lb) 22 2217 16 Horizontal Seal Strength (lb/inch) 9.4 9.1 7.0 6.8 Seal Thinning   2.1%    3.0% >20% >20% Stiffness (1% Modulus in lb) 170  170  100 103  Glopak Drop Test (# of times) 7-9 7-9 2-4 2-4

[0060] The above are typical values obtained from representativesamples, DG 2 and DG 10 are Glopak experimental multi-layer films. Comp1 and Comp 2 are competitive mono-layer films used in Canadian dairies.

[0061] It is within the ambit of the present invention to cover anyobvious modifications provided these fall within the scope of theappended claims.

We claim:
 1. A multi-layer film structure for use in packaging flowabledairy products into flexible pouches comprising an inner sealing layer,an outer layer, and a core sandwiched between said sealing layer andsaid outer layer, wherein said sealing layer comprises about 40 to 100%weight percent of a metallocene resin having a density of between about0.902 and 0.9122, and about 0 to 60 weight percent of a low densitypolyethylene or a mixture of low density polyethylene and linear lowdensity polyethylene, said outer layer comprises a low densitypolyethylene or a mixture of low density polyethylene and linear lowdensity polyethylene, said core comprising a mixture of about 20 to 90weight percent of a polypropylene copolymer and about 10 to 80 weightpercent of a low density polyethylene or a mixture of low densitypolyethylene and linear low density polyethylene, said multi-layer filmstructure having a thickness within a range between about 50 and 70microns (2.0-2.75 mil).
 2. A multi-layer film structure according toclaim 1, wherein said sealing layer represents about 10 to 30 weightpercent of said structure.
 3. A multi-layer film structure according toclaim 1, wherein said core represents about 30 to 70 weight percent ofsaid structure.
 4. A multi-layer film structure according to claim 1,wherein said outer layer represents about 10 to 30 weight percent ofsaid structure.